262 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



Malpighian pyramids, but sends prolongations be- 

 tween them down to the renal sinus. These cortical 

 prolongations are called the columns of Bertini, of 

 which there are as many as there are Malpighian 

 pyramids. 



It is convenient to describe the kidney tubules as 

 consisting of nine parts. Each tube commences in 

 the labyrinth of the cortex with (i) an invaginated 

 dilatation called Bowman's capsule. This capsule 

 is lined by simple squamous epithelium which, 

 when invaginated, makes two layers, the lumen of 

 the tube being between these layers. Into the in- 

 vaginated cavity is crowded a tuft of blood capil- 

 laries called a glomerulus. A liberal supply of con- 

 nective tissue blends with these capillaries. The 

 capsule and glomerulus are frequently called a 

 Malpighian corpuscle. At the base of the cap- 

 sule each tube is constricted, forming (2) the neck, 

 after which it becomes much convoluted and wide, 

 forming (3) the proximal convoluted tubule. The 

 cells of this part are large with very thin cell 

 walls. The cytoplasm immediately around the nu- 

 cleus is granular, but toward the basement membrane 

 it is striated with lines at right angles to the mem- 

 brane. The tube now approaches the medulla, 

 becomes nearly straight, but rapidly narrows to 

 form (4) the spiral portion. It now passes straight 

 down a Malpighian pyramid, where it makes a short 

 curve, and returning thus forms (5) the loop of 

 Henle. This loop has a narrow descending limb 

 with a short curve, and a wider ascending limb. 

 The narrow descending limb and curve has simple 



